Java 潜规则收集

有 goto 关键字却不能用？

getout:{
    for (int i = 0; i < N; ++i) {
        for (int j = i; j < N; ++j) {
            for (int k = j; k < N; ++k) {
                break getout; // 打断循环跳到 OUT
            }
        }
    }
}
// OUT

enum 可以当类写

// 出自 Sun 的例子（Sun 真的很喜欢太阳系，但他们不知道冥王星已经出局了么？）
public enum Planet {
  MERCURY (3.303e+23, 2.4397e6),
  VENUS   (4.869e+24, 6.0518e6),
  EARTH   (5.976e+24, 6.37814e6),
  MARS    (6.421e+23, 3.3972e6),
  JUPITER (1.9e+27,   7.1492e7),
  SATURN  (5.688e+26, 6.0268e7),
  URANUS  (8.686e+25, 2.5559e7),
  NEPTUNE (1.024e+26, 2.4746e7),
  PLUTO   (1.27e+22,  1.137e6);

  private final double mass;   // 质量/千克
  private final double radius; // 半径/米
  Planet(double mass, double radius) {
      this.mass = mass;
      this.radius = radius;
  }
  public double mass()   { return mass; }
  public double radius() { return radius; }

  // 重力常数/(立方米每千克秒平方)
  public static final double G = 6.67300E-11;

  public double surfaceGravity() {
      return G * mass / (radius * radius);
  }
  public double surfaceWeight(double otherMass) {
      return otherMass * surfaceGravity();
  }
}

// 如何使用
public static void main(String[] args) {
    Planet pEarth = Planet.EARTH;
    //..
    pEarth.radius();
    pEarth.surfaceGravity();
    pEarth.surfaceWeight(12.0);
    //..
}

双花实例初始化块

Map map = new HashMap() {{
    put("a key", "a value");
    put("another key", "another value");
}};

在代码中直接写 URL

class Example {
  public static void main(String[] args) {
    http://www.iteye.com
    System.out.println("Hello World!");
  }
}

如果在函数 return 后还要做些事情……

try { return 1; }
finally { System.out.println("Bye!"); }